We plan to study the structures of a number of antibiotics, biologically active peptides, and marine natural products, employing mass spectrometry as the principal structural tool. Most of the compounds to be studied (marine natural products from tunicates, gorgonians and sponges, antibiotics including saramycetin, CC 1014 and the zorbonomycins) have potent antiviral, antimicrobial, or antitumor activity. Others, the peptaibophol antibiotics and calciphorin, a peptide, assist ion-transport across membranes, while coherin, a peptide, is reputed to regulate intestinal motility and pyochelin, a peptide, stimulates the growth of Pseudomonas aeruginosa.